The Fender circuit

[mcilfilm]

Hey guys.

I been enjoying this forum for the past couple of weeks and wanted to thank you all again.

I've been building HiFi amps for a while and finished my first guitar amp build
(5e3) and ready to start another. These are a blast.
I just read a neat little article on guitar amp theory. Really enjoying this.

Looking forward to doing a scratch build in the near future on another of the Fender circuits.

What I was wondering is this:

Does anyone want to take a minute to describe the differences between the fender circuits and the Marshall type circuits in terms of layout and the effects on sound etc?

I've built a lot of amps with a degree of success but I'm not a master builder who knows a ton. Just a good listener and question asker.
I'm just recently infatuated with the Fender type circuits.

Again thanks a ton.(metric ton)

Rob

[mcilfilm]

Or a link to a good article on the subject of the early fender circuits and why they are different and sound different from the Marshall type amps.

Thanks tons.

[NickC]

Here is a great book on the Fender 5F6-A Bassman, which is very similar to the Marshall JTM45.

http://www.amazon.com/Circuit-Analysis- ... 0976982250

Might be able to get it through your local library (though they may have to borrow it from another library). Or, you might want a copy for your own library.

The book is heavy on math and deep circuit analysis. Heady stuff.

[matt h]

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[M Fowler]

My favorite is a JCM800 2204 50watt because I can gig any type of music I want with this amp from country, blues, to Rock and you have the Master Volume to make it easy.

I build them as 1-12" speaker combo type.

Mark

[roberto]

Mark, what B+ for EL34, PI and preamp you prefer for that circuit?

[shocki]

Great post Matt! Thanks alot. I am thinking about why a Marshall sounds like a Marshall thing right now.

Would you think the cathode follower also has a major impact? Or is it more the position of the tone controls in the signal chain?

I currently modded my BF Bassman first channel to sound more like a Marshall. So I moved the tonestack after the preamp stages.

Basicly like in this schematic.
http://rh-tech.org/public/18-Watt/18_Wa ... ematic.gif

It sounds more Marshally then before. But I am not quite there yet
I will have to try the cathode follower I guess and also try the AX7 in the PI (but this will change the sound the Blackface channel of this amp what I try to avoid)

Other than that I will add a feedback pot. This could also influence the sound. Another difference is the presence pot.

I am also thinking about filtering and voltages at the moment.

[M Fowler]

Mark, what B+ for EL34, PI and preamp you prefer for that circuit?

I like to use Magnetic Components Plexi iron so 450v-460v plates of EL34's and around 250v on pI anodes.

[roberto]

Thank you Mark, same voltages I prefer for that amp:
460 V on plates of EL34s and 250-280V on PI.

[matt h]

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[shocki]

If you want to switch to a 12ax7 PI, it's not that difficult.

Did not even know I have to switch something. I though just swapping out tubes would be OK? Maybe I could change the tail resistor from 22k to 10k. But i am not sure if this will have a huge effect.

[matt h]

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[shocki]

This is what I am having right now. Looks pretty similar expect for the "fizz cap"

http://thevintagesound.com/ffg/schem/ba ... _schem.gif

[matt h]

(deleted)

[shocki]

I changed the whole preamp to CF now and it sounds much better. Warmer and not agressive at all.

I can't make out the value of the bias resistor, it appears to be 270ohm?

I am using 470 at the moment.

The 500pF "entrance" cap to the PI from the preamp input side would also do some icky things to a marshally preamp, which is already on the bright side.

Mhh. I thought a bigger value here means more bass? Didn't know that this deals with the treble also? I am using 0.01uF here.

When you change the feedback circuit, you're also going to want to change the tail resistor.

You mean the 10k that is normally in the Marshalls?
When I change this from 22k to 10k and playing around with the calculator I only see very slight changes in gain.
http://www.ampbooks.com/home/amplifier- ... iled-pair/